Since blood is carried from the heart to all of your body's tissue and organs in vessels called arteries, blood pressure is the force of the blood pushing against the walls of those arteries. In fact, each time the heart beats (about 60-70 times a minute at rest), it pumps out blood into the arteries. Your blood pressure is at its greatest when the heart contracts and is pumping the blood. This is called systolic pressure. When the heart is at rest, in between beats, your blood pressure falls. This is the diastolic pressure.

Blood pressure is always given as these two numbers, systolic and diastolic pressures. Both are important. Usually they are written one above or before the other, such as 120/80 mm Hg, with the top number the systolic, and the bottom the diastolic.

Different actions make your blood pressure go up or down. For example, if you run for a bus, your blood pressure goes up. When you sleep at night, your blood pressure goes down. These changes in blood pressure are normal.

Some people have blood pressure that stays up all or most of the time. Their blood pushes against the walls of their arteries with higher-than-normal force. If untreated this can lead to serious medical problems like these:

• Arteriosclerosis ("hardening of the arteries"). High blood pressure harms the arteries by making them thick and stiff. This speeds the build up of cholesterol and fats in the blood vessels like rust in a pipe, which prevents the blood from flowing through the body, and in time can lead to a heart attack or stroke.
• Heart Attack. Blood carries oxygen to the body. When the arteries that bring blood to the heart muscle become blocked, the heart cannot get enough oxygen. Reduced blood flow can cause chest pain (angina). Eventually, the flow may be stopped completely, causing a heart attack.
• Enlarged heart. High blood pressure causes the heart to work harder. Over time, this causes the heart to thicken and stretch. Eventually the heart fails to function normally causing fluids to back up into the lungs. Controlling high blood pressure can prevent this from happening.
• Kidney Damage. The kidney acts as a filter to rid the body of wastes. Over a number of years, high blood pressure can narrow and thicken the blood vessels of the kidney. The kidney filters less fluid, and waste builds up in the blood. The kidneys may fail altogether. When this happens, medical treatment (dialysis) or a kidney transplant may be needed.
• Stroke. High blood pressure can harm the arteries, causing them to narrow faster. So, less blood can get to the brain. If a blood clot blocks one of the narrowed arteries, a stroke (thrombotic stroke) may occur. A stroke can also occur when very high pressure causes a break in a weakened blood vessel in the brain (hemorrhagic stroke).

Checking your Blood Pressure

Having your blood pressure checked is quick, easy, and painless. Your blood pressure is measured with an instrument called a sphygmomanometer (sfig-mo-ma-nom-e-ter).

It works like this: A blood pressure cuff is wrapped around your upper arm and inflated to stop the blood flow in your artery for a few seconds. A valve is opened and air is then released from the cuff and the sounds of your blood rushing through an artery are heard through a stethoscope. The first sound heard and registered on the gauge or mercury column is called the systolic blood pressure. It represents the maximum pressure in the artery produced as the heart contracts and the blood begins to flow. The last sound heard as more air is released from the cuff is the diastolic blood pressure. It represents the lowest pressure that remains within the artery when the heart is at rest.

What Do the Numbers Mean?

Blood pressure is always expressed in two numbers that represent the systolic and diastolic pressures. These numbers are measurements of millimeters (mm) of mercury (Hg). The measurement is written one above or before the other, with the systolic number on the top and the diastolic number on the bottom. For example, a blood pressure measurement of 120/80 mm Hg is expressed verbally as "120 over 80." See the table below which shows categories for blood pressure levels in adults.

If your blood pressure is less than 140/90 mm Hg, it is considered normal. However, a blood pressure below 120/80 mm Hg is even better for your heart and blood vessels. People use to think that low blood pressure (for example, 105/65 mm Hg in an adult) was unhealthy. Except for rare cases, this is not true. High blood pressure or "hypertension" is classified by stages and is more serious as the numbers get higher.

CATEGORIES FOR BLOOD PRESSURE LEVELS IN ADULTS*

(Age 18 Years and Older)

Blood Pressure Level (mm Hg) : Category Systolic Diastolic

• Normal <130 <85
• High Normal 130-139 85-89
• High Blood Pressure
• Stage 1 140-159 90-99
• Stage 2 160-179 100-109
• Stage 3 >180 >110